Heisenberg exchange enhancement by orbital relaxation in cuprate compounds

TL;DR

This study calculates the Heisenberg exchange in cuprate compounds, revealing that orbital relaxation significantly enhances antiferromagnetic interactions, with results closely matching experimental data.

Contribution

It demonstrates that orbital relaxation during charge transfer states plays a crucial role in enhancing exchange interactions in cuprates, a novel insight in the field.

Findings

Orbital relaxation significantly increases exchange interaction strength.

Close agreement between calculations and experimental data.

Charge transfer states are key to understanding magnetic properties.

Abstract

We calculate the Heisenberg exchange J in the quasi-2D antiferromagnetic cuprates La2CuO4, YBa2Cu3O6, Nd2CuO4 and Sr2CuO2Cl2. We apply all-electron (MC)SCF and non-orthogonal CI calculations to [Cu2O11]18-, [Cu2O9]14-, [Cu2O7]10- and [Cu2O7Cl4]14- clusters in a model charge embedding. The (MC)SCF triplet and singlet ground states are well characterized by Cu2+ (dx2-y2) and O2-. The antiferromagnetic exchange is strongly enhanced by admixing relaxed (MC)SCF triplet and singlet excited states, in which a single electron is transferred from the central O ion to Cu. We ascribe this effect to orbital relaxation in the charge transfer component of the wave function. Close agreement with experiment is obtained.